Page images

is caught the trap presently re-opens of itself, and is ready for another attempt. With regard to the object of this strange proceeding, there can be no doubt that the insect is retained until the softer parts of the body are completely dissolved in the thick mucous fluid which is exuded by the leaves : and Professor Asa Gray considers that the evidence is nearly complete that the animal matter is actually absorbed in the leaf itself. It is even stated that pieces of raw beef are digested by the leaf in the same manner! Seeing, however, that it is now generally admitted by physiologists that even pure water is not absorbed through the pores of leaves, which serve only for the exhalation of vapour, this explanation is very hard of belief. The “pitchers” of the Nepenthes, or pitcher-plant, act also as fly-traps, large numbers of insects being enticed into them by the fluid they secrete, and are then unable to extricate themselves.

The sensitiveness of the leaves of plants is but an excessive development of the phenomenon known as the Sleep of plants. In the case of the Sensitive Plant the position assumed by the leaf and leaflets in the night is the same as that which they assume when disturbed in the day-time; and with many other plants, such as the clover and the Robinia or “ acacia” tree, the change in the position of the leaflets, morning and evening, is a familiar fact. The Sleep of Plants extends also to the flowers, many plants opening their flowers only at particular times of the day. Thus the major convolvulus of the gardens and the goat's-beard open at sunrise and always close by about noon, the evening primrose opens only in the evening, and many others last for but a single day. So regular is the time of opening and closing of some flowers, that Linnæus drew up a list, which he termed a “ floral clock.” The singular part of the affair is, that with many flowers the time of opening and closing is determined, not by the degree of light, or by the temperature or humidity of the atmosphere, but absolutely by the hour of the day. The giant water-lily of the Amazons, the Victoria regia, opens, for the first time, about 6 P.m., and closes in a few hours, then opens again at 6 A.M. the next day, remaining open until the afternoon, when it closes and sinks below the water. Other plants, again, open their flowers only in the bright sunshine, as the beautiful yellow centaury or Chlora perfoliata, the sundew, Drosera rotundifolia, &c. In the latter plant, belonging to the same natural order as the Venus's Fly-trap, and possessing a slight irritability of the leaves, Mr. Worthington Smith has noticed also a strong sensitiveness in the petals, the flowers closing suddenly when touched.

Irritability or sensitiveness, similar to that of the leaves of

list, wair is, thatwned, not by thatmosphere, the Amazons, and

the Sensitive Plant, is not uncommon in the flower. An instance has been alluded to in the petals of the sundew; it occurs also in the lip of the corolla of several of the orchis tribe. It is, however, more common in the proper organs of reproduction, as the style of Stylidium, the stamens of the berberry, &c., and is then directly connected with the process of fertilisation of the ovule. In Stylidium, an Australian genus, the style and filaments are adherent into a column, which hangs over on one side of the flower. When touched, it rises up and springs over to the opposite side, at the same time opening its anthers and scattering the pollen. The stamens of the various species of Berberis and Mahonia, to the former of which our common berberry belongs, exhibit this irritability to a remarkable degree. If touched with a pin or other object at the base of the inside face of the filament, the stamen will spring violently forward from its place within the petal, so as to bring the anther into contact with the stigma, as shown in fig. 4, and will after a time slowly resume its original position. At first sight it may seem as if this contrivance were intended to ensure the fertilisation of the pistil from the pollen of its own flower. In reality, however, the reverse is the case ; the excitation takes place in nature when an insect entering the flower for the sake of the honey in the glands at the base of the pistil, touches the inside of one of the stamens. The pollen is thus thrown on to the head or body of the insect, which carries it away to the next flower it visits, and leaves some of it on the stigma, and thus crossfertilisation instead of self-fertilisation is secured. Similar motion of the stamens towards the pistil, but spontaneous, takes place in the case of the London Pride, and other species of Suxifraga.

Elasticity is, indeed, a common property of organised tissue, though it is not often developed to so evident an extent. In the “ touch-me-not," or Impatiens, we have a familiar instance in the seed-vessel, which, if touched when nearly ripe, suddenly coils back, throwing the seeds to a considerable distance. The “ squirting cucumber” (Momordica Elaterium) marks the period of ripeness by the fruit separating from its stalk, and expelling the seeds and juice with great violence. Mr. Thomas Meehan described a remarkable instance of elasticity at a recent meeting of the Academy of Natural Sciences of Philadelphia. The seeds -or, as would appear from his description, more correctly the embryos of the seeds of the American switchhazel” (Hamamelis virginica) are thrown out with such force as to strike people violently in the face who pass through the woods. Collecting a number of the capsules, and laying them on the floor, he found the seeds or embryos were thrown out generally to the distance of four or six feet, and in one instance as much as twelve feet.

Many of the instances of spontaneous motion or irritability we have now recorded may doubtless be explained by the application of known physical laws. With others this is not so easy; and it is but reasoning in a circle to say that because the organisms which manifest them belong to the vegetable kingdom, therefore the phenomena cannot be the result of a sentient force acting upon, and independent of, matter. Darwin has described how certain movements of the tendrils of climbing plants would be termed instinctive if they were observed in animals. The rapid rotatory motion of the zoospores of the lower Algæ is absolutely undistinguishable from that of certain undoubted lowly organised forms of animal life. It is very difficult to distinguish between the movement of a shoot of a climber performing its circles in the air in search of a support, and that of the tentacula of a coral-polyp in search of food. The mode in which the Venus's Fly-trap seizes and encages its prey is very like that adopted by a sea-anemone. Every fresh addition to our knowledge seems to confirm us in the view that it is unwise to dogmatise by laying down too rigid generalities, and absolutely to deny certain functions to whole classes of animated beings because we do not find them exhibited in the forms most familiar to us. I do not wish distinctly to claim for plants the actual possession of a voluntary or sentient faculty. But I do wish to point out that facts do not support us in asserting that a clear line of demarcation separates the animal from the vegetable kingdom; the power of voluntary motion belonging to the one and not to the other. Taking all the facts we have described into consideration, the statement seems justified which has been made by one of our most experienced naturalists, Professor Wyville Thomson* :-“ There are certain phenomena, even among the higher plants, which it is very difficult to explain without admitting some low form of a general harmonising and regulating function, comparable to such an obscure manifestation of reflex nervous action as we have in sponges and in other animals in which a distinct nervous system is absent.” †

• Introductory Lecture to the Natural Ilistory Class at the University of Edinburgh, May, 1871. See “ Nature," vol. iv. p. 91.

† Since writing the above, I have met with the following remarks by the Italian botanist, Prof. Delpino (“American Naturalist,” July, 1871, p. 297):-“I must here, as always, declare myself a teleologist and a vitalist. Now teleology and vitalism, far from being vanquished by the Darwinian doctrine, find in it their most solid support. What do teleology and vitalism mean? They mean that we believe that there is in all living things an


Fig. 1. Leaf of Sensitive Plant, Mimosa predica ; a, in normal position; b,

after depression by the approach of the hand. „, 2. Leaves of Venus's Fly-trap, Dionæa muscipula, one of them closed on

an imprisoned fly. „ 3. Tendril of Virginian Creeper, Ampelopsis virginica ; a, before contact;

b, after contact with a wall. „ 4. Stamen of Berberry, Berberis vulgaris ; a, normal position; b, after

excitation of base of filament. » 5. Zoospores of Algæ ; a, b, Conferva ; c, Vaucheria. „ 6. Spermatozoa; a, Chara; b, Sea-weed, Fucus serratus.

innate, specific principle, intelligent, free, and teleological. This principle is the hidden cause of the variability of organised beings, as well as the wonderful harmonies which have been established between one being and another." NEWS FROM THE STARS.


TROM time to time, during the last three years, I have T brought before the readers of this magazine the various arguments and considerations on which I have based certain new views respecting the constitution of the sidereal universe. In so doing I have had occasion to deal chiefly with facts already known, though not hitherto viewed in that particular light in which I sought to place them. Indeed it is an essential part of my general argument that much that is contained in observations already made has been escaping us. In the eagerness of astronomers to ascertain new facts, they have been neglecting the interpretation of facts already ascertained.

But I have long felt that it would greatly tend to advance the new views which I have advocated, if some process of research, pursued by one of those astronomers of our day who possess the requisite means and leisure for prolonged enquiries, should confirm in a clear and decisive way some definite point of my new theories. Thus, if new observational evidence should be found in favour of my theory that the nebulie are not external to our galaxy, or if new evidence should be obtained to show that the stars are aggregated in certain regions within our system and segregated from others; or again, if my theory of star-drift should be confirmed by new and striking evidence, I felt that a greater measure of coufidence in my analysis of former evidence would thenceforward be accorded. I had no occasion, indeed, to complain of cavil or opposition; in fact, a degree of attention had been given to the new opinions I advocated which was certainly much greater than I had looked for. But there must always he such an inertia in the general weight of opinion in favour of accepted views, that only a steady reiteration of reasoning during a long period, or else some striking and impressive discovery, can cause the weight of opinion to tend in the contrary direction.

« PreviousContinue »